Greek police fired tear gas and water cannons to disperse thousands of protesters who flooded into the main square before parliament in a massive show of anger against politicians who were due to narrowly pass an austerity package.

The violence erupted as a handful of protesters tried to break through a barricade to enter parliament, where prime minister Antonis Samaras was expected to barely eke out a win for the belt-tightening law despite opposition from a coalition partner.

The parliamentary session was briefly interrupted when parliament workers went on strike and opposition politicians walked out of the chamber in protest.

Outside parliament, loud booms rang out as protesters hurled petrol bombs and police responded with tear gas and stun grenades. Smoke and small fires could be seen on a street next to parliament.

That came after a sea of Greeks braved a steady downpour holding flags and banners saying “It’s them or us!” and “End this disaster!” stood before riot police guarding parliament.

In all, nearly 100,000 protesters — some chanting “fight, they’re drinking our blood” — packed the square and side streets in one of the largest rallies seen in months, police said.

Protesters held aloft Italian, Portuguese and Spanish flags in solidarity with other southern European nations enduring austerity.

“These measures are killing us little by little and lawmakers in there don’t give a damn,” said Maria Aliferopoulou, a 52-year-old mother of two living on €1,000 a month.

“They are rich, they have everything and we have nothing and are fighting for crumbs, for survival.”

Public transport was halted, schools, banks, and government offices were shut, and rubbish was piling up on streets on the second day of a two-day nationwide strike, called to protest against the vote.

Backed by the leftist opposition, unions say the measures will hit the poor and spare the wealthy, while deepening a five-year recession that has wiped out a fifth of the country’s output and driven unemployment to a record 25%.